High Velocity with a short barrel concerns?

[TimberHunter]

Rifle: CA 308 20” 1-10” twist barrel with suppressor

Bullet: 155 lapua Scenar
Brass: New Lapua

Reloaded H4895 43grain to 46 grains. 1 reload at 43.0, 1 at 43.5, 1 at 40.0, etc up till 46. I was looking for pressure signs to see what kind of velocity I could get

I used Hodgdon data and 155 Sierra BTSP. Per hodgdon , with a 24” barrel, velocity from 2,735 to 2,873.

FPS recorded this afternoon in 45 degree weather
43: 2739
43.5: 2827
44: 2825
44.52857
45:2890
45.5:2915 very faint ejector mark on lapua brass
46: 2937 slightly sticky bolt

44,44.5,45 all shot into a a small hole that measures around 1/2” at 115 yards

I like the velocity and grouping but these speeds out of a 20” barrel concern me because I’m getting over book velocity with 4” less of barrel. But I’m not seeing any obvious signs of pressure (no distinct ejector Mark, no larger craters in the primers, no hard to open bolt)

Do I need to back it down so I’m within book velocities minus about 75-100 FPS for my 20” barrel?


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[83cj-7]

No need to back down. You just got blessed with a fast barrel. Seems that is accurate as well.

I helped two brother that I know get dope on their .308 rifles for a class. One had a 16” barrel and the other had a 24” barrel. They were shooting from the same case of Federal Gold Medal 168. The 16” barrel shot 2650 and the 24” shot 2600. Just variation in barrel or how the throat was cut in the chamber.

 

[sneaky]

You used book data for 2 different projectiles. You aren't going to be able to make a direct correlation. Those guidebooks are for reference....a starting point. Your own test showed you that. You may also have a naturally fast barrel.

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[TimberHunter]

You used book data for 2 different projectiles. You aren't going to be able to make a direct correlation. Those guidebooks are for reference....a starting point. Your own test showed you that. You may also have a naturally fast barrel.

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The 155 Sierra HPBT is the closest bullet to the 155 Scenar I could find published data on. I happen to have both bullets and the Sierra measures approx .025” shorter then the Scenar. Taking that into account, I seated the Sceanrs to 2.800 OAL

I thought that would make an apples to apples comparison as far as pressure and velocity. Maybe I’ll have to load up some 155 Sierras and see if I get the same result in velocity.

But if I was over pressured, wouldn’t I see it in the primers and ejectors marks on the new Lapua brass?


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[B23]

I run your loads through QL and where you start to see pressure signs is exactly where QL shows your loads are starting to get beyond recommend SAAMI max chamber pressure.

Your velocity is a little higher than the QL predictions but there's a lot of things that can affect that and not really anything to be concerned about so I'd say you're good to go.

 

[TimberHunter]

I run your loads through QL and where you start to see pressure signs is exactly where QL shows your loads are starting to get beyond recommend SAAMI max chamber pressure.

Your velocity is a little higher than the QL predictions but there's a lot of things that can affect that and not really anything to be concerned about so I'd say you're good to go.

Thank you sir! If you don’t mind, would you be able to run 44.5grs and 45 grains through QL and reply with what pressures it shows? I saw no obvious pressure signs at those loads and I’m considering picking between those charges for my hunting load

I need to buy QL, which version do you use? They have some that are $152 and some that are $55


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[B23]

SAAMI Max 62,000 /44.5=61,084/45.0=63,333

Remember, QL like a loading manual and though often very accurate and close is still just a guide certainly nothing absolute and the information it gives you is only as accurate as the information you input into the program. Things like actual case capacity versus using default capacities and if you're seating bullets out to touch or near touch can have substantial affects on pressure.

Software NECO Shop Online | Neconos.com

www.neconos.com

 

[TimberHunter]

SAAMI Max 62,000 /44.5=61,084/45.0=63,333

Remember, QL like a loading manual and though often very accurate and close is still just a guide certainly nothing absolute and the information it gives you is only as accurate as the information you input into the program. Things like actual case capacity versus using default capacities and if you're seating bullets out to touch or near touch can have substantial affects on pressure.

Software NECO Shop Online | Neconos.com

www.neconos.com

Thank you again sir! I ordered it but it’s shipping out of Germany so it is going to take a while to get to me.

When you input the data into QL, you input Lapua brass with Lapaua 155 Scenar seated at 2.800 with H4895 correct?


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[B23]

When you input the data into QL, you input Lapua brass with Lapaua 155 Scenar seated at 2.800 with H4895 correct?

That is correct.

It uses a default case capacity of 56gr H20 but your cases may be slightly different. If they are less pressure will be raised along with velocity and if they are more then the opposite.

QL takes a little while to get the hang of what it's all capable of. I've had it for years and I'm still learning new things about it but I've found it to be a very useful tool.

 

[TimberHunter]

That is correct.

It uses a default case capacity of 56gr H20 but your cases may be slightly different. If they are less pressure will be raised along with velocity and if they are more then the opposite.

QL takes a little while to get the hang of what it's all capable of. I've had it for years and I'm still learning new things about it but I've found it to be a very useful tool.

Weighted case capacity of h20 in lapaua once shot brass from my chamber with spent primers in them:

53.2
54
54.2
54.4
54.5
54.6
54.8
54.9

The higher case capacity came from the brass that was loaded with more powder, makes sense since the brass likely formed to the chamber more closely with the higher powder/pressure.

Long story short QL isn’t going to work on my MAC computer (talked to the sellers of QL). Could you please rerun the numbers with let’s say 54.5 grains of H20 capacity


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[Red Letters]

These guys shoot real short barrels and have experimented with all kinds of options, if you are interested in reading. (this is a pdf I've seen several write ups from them this just happen to be the first search that popped up) GPS sniper school out of Arizona

https://dilloncdn.com/bluepress/july_09_p60_short_p1.pdf

 

[TimberHunter]

B23,

When you get a chance could you please run the numbers with 54.5 grains of water capacity in the Lapua brass?


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[B23]

B23,

When you get a chance could you please run the numbers with 54.5 grains of water capacity in the Lapua brass?


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Changing the case capacity to match your brass versus using the default bumped up your pressures and naturally your FPS estimates as well. The velocity estimate QL shows, now with the adjusted case capacity, is pretty close to what you are actually getting.

44.5gr = 65642 PSI chamber pressure / 2820FPS

45.0gr = 68156 PSI / 2850FPS

 

[TimberHunter]

Changing the case capacity to match your brass versus using the default bumped up your pressures and naturally your FPS estimates as well. The velocity estimate QL shows, now with the adjusted case capacity, is pretty close to what you are actually getting.

44.5gr = 65642 PSI chamber pressure / 2820FPS

45.0gr = 68156 PSI / 2850FPS

Thank you sir! From my research, people have recommended sticking with 5% below max when using Lapua because of the lower case capacity so that makes sense now that I have the numbers you provided.

Those pressures are a little concerning to me when max sammi is 62k psi. Any idea why my brass isn’t showing signs of pressure? I slowly shot all the way up to 46 grains the other day (book max) which should be in the ball park of 73k psi...? But no obvious pressure signs other than slightly stiff bolt. Yikes...


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